To deliver messages published to a topic to subscription endpoints, you must add the endpoints to the topic.
on the upper left to select the desired region and project.The SMN console is displayed.
In the navigation pane, choose Topics.
The Topics page is displayed.
The Add Subscription box is displayed.

Enter a valid email address, for example, username@example.com.
Subscribers will receive a subscription confirmation email valid in 48 hours and must confirm the subscription to receive messages published to the topic.
Enter a public network URL, for example, http://example.com/notification/action. HTTP/HTTPS subscribers must confirm their subscriptions. For details about HTTP/HTTPS messages, see section A.6.1 Introduction.
Enter a valid mobile number preceded by a plus sign (+) and a country code, for example, +4900000000.
Subscribers will receive a subscription confirmation message valid in 48 hours and must confirm the subscription to receive messages published to the topic.
Subscription endpoints are message queues. This type of subscriptions does not need confirmation. Click
to select subscription endpoints. Ensure that the queue policy grants the DMS:ProduceMessages permission to SMN. For details, see "Managing Queue Policies" in the Distributed Message Service User Guide.
The subscription you added is displayed in the subscription list.